The invention relates to the methods of extruding a plastic spacer directly on an object, in particular on the periphery of a window glazing such as an automobile glazing intended to be glued into the opening of a vehicle. It relates more specifically to the operations of finishing a spacer in a loop, i.e., when the extrusion of the spacer ends on the object in the place where it began. It is particularly exacting to produce properly the connection zone between the end and the beginning of the extruded spacer. The invention proposes a new method to complete this connection.
The method of depositing an elastomer frame on a glazing by means of extrusion has been described before, particularly in U.S. Pat. Nos. 4,571,278 and 5,336,349. They show an extrusion head that is relatively moved in relation to the glazing, where it deposits a viscous material that hardens after it is deposited. Another patent, EP-A-493068, shows a method where the extrusion head is fixed and the glazing is moved in front of it.
One exacting aspect of the method of in situ extrusion on the periphery of glazing is the final phase in cases where the frame is closed, i.e., when the spacer that is deposited on the glazing makes a loop. In the connection zone, the end of the extruded spacer must meet up with the beginning of the same spacer to close the loop. If no technical measures are taken, the connection zone will be misshaped. When tolerances are precise or if the elastomer spacer is visible on the installed glazing, it is impossible to leave the connection unchanged.
Three different methods have been proposed to solve this problem. The first method is described in U.S. Pat. No. 5,057,265 and it corrects the form of the connection immediately after it has been formed, while the elastomeric material is still viscous and malleable. The two other methods substitute an object of the correct form for the misshapen spacer that has already hardened. Of those two aforementioned methods, the one mentioned in EP-A 493 068 substitutes for the poorly-formed spacer a hardened product that has been extruded elsewhere by a traditional method. This separately-formed hardened product is then glued to the glazing to complete the loop. The last method described in document EP-A-524 060 proposes substituting for the poorly-formed spacer a spacer that is hardened in place. This present invention comprises an improved variation of that method.
U.S. Pat. No. 5,316,829 suggests removing the poorly-formed part and then placing on the zone concerned a mold element that connects the two sides of the properly-shaped spacer and injecting a material that hardens in place and recreates the spacer in the place where the poorly-formed part was removed. The disadvantage of the latter method is that it requires re-work of the glazing after it has left the extrusion station so that it can undergo a new production phase, i.e., the injection of the new material. This complicates and delays the production of the completed glazing.
The technical problem that the invention is intended to overcome is, in contrast to the three preceding methods, that most of the operation of correcting the connection zone can be done at the time of extrusion.